Differential amplifiers and special instrumentation amplifiers are used for the amplification of a wide array of signals in broad fields of application. As microphone amplifiers, they combine low noise with a high dynamic range. Audio applications alone require such high dynamic ranges on the order of magnitude of 100 dB. In contrast, in mobile applications, such as, for example, in hearing aids and cellular telephones, the power supply voltage typically equals 1.6 V and thus limits the maximum achievable signal amplitude to approximately 1.4 V (Peak to Peak). This corresponds to an amplitude of approximately 1 Vrms. Due to ongoing miniaturization, it is to be expected that the power supply voltages in the future must be reduced even further.
In most applications, it is now necessary that a preamplifier features a large signal amplification. In this way, the noise of the subsequent stages is suppressed, which has advantageous effects for all of the subsequent signal processing steps. The amplification is typically implemented with variable amplification factors from 3-100. In order to simultaneously fulfill the requirements on amplification, dynamic range, and variable signal amplitudes and in this way keep distortion for large signal amplitudes as small as possible, it is necessary to provide an amplification compression or an automatic gain control (AGC) circuit in the preamplifier.